During the drilling of oil wells which traverse earth formations it is necessary to make deductive evaluations based on inferences which can be drawn from the measurement of parameters at various depths of the well bore. Obviously the degree of accuracy of the measurement of the parameters affects the validity of the deductions or calculations made from the measurements. The parameters of pressure and temperature are two significant measurements which are made in a borehole and from which evaluation of the geophysical characteristics of the contents of the earth formation can be made.
Heretofore, pressure and temperature measurements have been routinely made with a variety of tools. A well known tool for measuring pressure and for obtaining a fluid sample from the earth formations is a Formation Tester. Where the tester is adapted to obtain a number of measurements or fluid samples it is sometimes called a multiple sample formation tester. One such tool for taking multiple samples is illustrated in U.S. Pat. No. 3,780,575 issued to Harold Urbanosky on Dec. 25, 1973. As illustrated in U.S. Pat. No. 3,780,575, a Formation Tester is adapted to be lowered into a well bore on an electrical armoured cable. At the desired location in the well bore where a test is desired, a sealing pad and back-up shoe are projected into engagement with the wall of a well bore. With the formation sealed off by the sealing pad, the formation is opened to a pressure chamber in the tool for a pressure measurement and, if desired, a sampling chamber is connected to the formation to obtain a fluid sample. Typical pressure measurements are made by pressure transducer of the mechanical or piezoelectric types. A measurement obtained by such types of transducers does not have precise accuracy and produces imprecise measurements.
Temperature measurements to obtain differential temperature measurements at spaced apart locations have been difficult to obtain because of the lack of response and sensitivity.
Accordingly, it is a feature of the present invention to provide new and improved bore hole measuring apparatus in which the measurements of temperature or pressure can be made in highly accurate fashion utilizing fiber optic technology.